In reference to single wire S.W. Antenna

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Hello,

I understand single wire antenna wires should be grounded. I have also
heard it is a good idea to put a lightening arrestor on them. Can someone
tell me a good type of lightening arrestor to get and how they are
connected, please ?

Wayne


Re: In reference to single wire S.W. Antenna

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Here is an example of how they are made and used.

http://www.geocities.com/n2uhc/lightningarrestors.html

Gnack

Re: In reference to single wire S.W. Antenna

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Thank You Gnack,

Now I have a better idea what they are all about.


Re: In reference to single wire S.W. Antenna

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Just a note: in the absence of an antenna terminal, one could take a couple
feet of insulated wire and attach it to the incoming signal line, then wrap
a few inches around the whip antenna, effectively coupling the incoming
signal to the whip inductively.  This is what I usually do, as it makes use
of the preamp between the whip antenna and the rest of the radio, giving you
better reception and audio.

Dave



Re: In reference to single wire S.W. Antenna

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....

Unless both ends of that wire are connected, one to the antenna and the
other to ground, making this one winding of a transformer, you are
actually using _capacitive_ coupling. The wire is one plate of the
capacitor, the whip is the other plate and the insulation is the
dielectric.  The body of the radio forms the plate of another capacitor
and the earth forms the second plate of that capacitor.

However, the name of the coupling mode is secondary to the fact that it
will provide stronger signals. However, connecting the antenna directly to
the whip will also work, and unless you take special precautions to
protect against lighting, direct or capacitive coupling are both almost
equally hazardous.

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                7w-110V light bulb
antenna -----|------UUU-------|-|------------antenna terminal of rx
            neon NE2          ^ v diodes opposite pollarity.
ground ------|----------------|-|------------ground terminal of rx

Something like the above diagram should work.

I had a nearby lightning strike that vaporized the antenna wire, burned
out the lightbulb and scattered pieces of the diodes around. The receiver
(a tube type) showed no damages.





--
bz        73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
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Re: In reference to single wire S.W. Antenna

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<snip>

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Be careful how you're looking at that for your understanding, though.
Something that appears to be a DC ground, need not be an AC (RF) ground. So
if you had a long wire antenna, and wrapped some turns around the telescopic
or whatever, and then grounded the hanging end, you have not grounded the
signals, because the turns around the telescopic form an inductance, which
serves to couple the signals into the radio, by induction. There are
caveats, of course, such as how many turns in your 'coil', the diameter of
the winding, the diameter of the wire, and the frequencies of interest. If
you look at the schematics for typical RF input stages, particularly with
higher frequency receivers, you will often see a coil of just a couple of
turns of quite thick wire connected directly to the antenna socket, which
you may initially think represents a 'short' to the antenna. If you take it
a stage further and start getting up into UHF and low SHF, you will often
find a straight piece of wire or even print connected directly across the
antenna input. At these frequencies however, that apparent 'short' is
actually an inductance, and may well have a reactance of several tens or
hundreds of ohms at the frequency of interest.

I have a home-brewed interdigital filter for 1.2GHz ATV lookback notching,
and the input and output coupling 'coils' are a single half-turn loop of 1mm
wire. The actual 'L' elements are straight pieces of 6mm ally rod.

Arfa



Re: In reference to single wire S.W. Antenna

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Hey Wayne,

When I built a homebrew RF amplifier to help pick up weak SW signals, I put
something together that I have actually seen work when lightening struck
somewhere nearby.  It consisted of a neon indicator light going from the
wire carrying the incoming signal to grount, and in parrallel with this I
put a 10K resistor (to bleed off static electricity at voltages below that
which would activate the neon indicator) and  two 1N4001 diodes, configured
so that if one did not conduct the other would (picture two arrows sitting
next to each other and pointing in opposite directions.)  Again, all of
these were in parrallel going from signal to ground, and then I put a .1uF
1000V ceramic disk capacitor  going from the signal side of all this to the
input of my amplifier (or to the input to the radio, in your case.)

The theory is that  the incoming signal will pass by all of this and go
through the .1uF capacitor to your radio, but a high-voltage pulse, such as
static electricity from someone touching the antenna wire or a nearby
lightening strike, will be stopped by the .1uF 1000V capacitor (make sure it
is a ceramic disk) and will be discharged by the neon indicator and one or
the other of the diodes, with tiny remnants of the pulse being blead off by
the 10K resistor.  Now, please understand , I am no expert (which someone
will no doubt point out) but I actually saw this work one time when I was
listening to a SW station while a storm approached.  I did not disconnect my
equipment before the storm got too close, and finally lightening struck
nearby and the neon indicator lit up for an instant.  That convinced me it
was time! :)  And I say that this whole thing worked because even though my
antenna picked up the pulse, it was discharged and my equipment did not
suffer any negative consequences.  I saw the neon indicator light up
briefly, and when putting this thing together that was something I never
actually expected to see.

In my opinion, the only thing one has to worry about with this setup is
losing some signal through the diodes, the PN junctions of which act as
small capacitors connecting the signal line to ground.  But I have not come
up with an answer to that yet.  Nothing is perfect...

If this interests you, write to me and I will email the schematic for it.

Hope this helps.  Take it easy...

Dave



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